How should I practice Process Refunds with Bounded Retries?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Mercor phone screen problems in FastPrep.

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FastPrep tags this as a Mercor phone screen coding practice problem when the problem catalog has that company and stage context.

Process Refunds with Bounded Retries

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Problem statement

Process independent refund requests. alreadyDone[i] tells whether request i was completed before this batch. attemptPatterns[i] lists the outcomes returned by successive payment attempts: S is success and F is failure.

If a request is already done, make zero attempts and return DONE:0. Otherwise make at most three attempts and stop on the first success. Return DONE:k after a success on attempt k. If every available attempt among the first three fails, return PENDING:k, where k is the number attempted.

Function

processRefundRetries(alreadyDone: boolean[], attemptPatterns: String[]) → String[]

Examples

Example 1

alreadyDone = [false,false,true]attemptPatterns = ["FFS","FFFF","S"]return = ["DONE:3","PENDING:3","DONE:0"]

A refund becomes done only after success, and an existing completion performs no attempt.

Example 2

alreadyDone = [false,false]attemptPatterns = ["S","FS"]return = ["DONE:1","DONE:2"]

The first success stops retries.

Example 3

alreadyDone = []attemptPatterns = []return = []

An empty batch has no results.

Constraints

0 <= alreadyDone.length == attemptPatterns.length <= 100000.
Every pattern has length from 0 through 100 and contains only S and F.
Requests are independent.